1. Field of the Invention
An electrosurgical device to generate a plasma stream to perform electrosurgery on a surgical target area on a patient.
2. Description of the Prior Art
High frequency electrical energy has been widely used in surgery. Tissue is cut and bodily fluids are coagulated using electrosurgical energy.
Electrosurgical instruments generally comprise “monopolar” devices or “bipolar” devices. Monopolar devices comprise an active electrode on the electrosurgical instrument with a return electrode attached to the patient. In monopolar electrosurgery, the electrosurgical energy flows through the active electrode on the instrument through the patient's body to the return electrode. Such monopolar devices are effective in surgical procedures where cutting and coagulation of tissue are required and where stray electrical currents do not pose a substantial risk to the patient.
Bipolar devices comprise an active electrode and a return electrode on the surgical instrument. In a bipolar electrosurgical device, electrosurgical energy flows through the active electrode to the tissue of a patient through a short distance through the tissue to the return electrode. The electrosurgical effects are substantially localized to a small area of tissue that is disposed between the two electrodes on the surgical instrument. Bipolar electrosurgical devices have been found to be useful with surgical procedures where stray electrical currents may pose a hazard to the patient or where other procedural concerns require close proximity of the active and return electrodes. Surgical operations involving bipolar electrosurgery often require methods and procedures that differ substantially from the methods and procedures involving monopolar electrosurgery.
Gas plasma is an ionized gas capable of conducting electrical energy. Plasmas are used in surgical devices to conduct electrosurgical energy to a patient. The plasma conducts the energy by providing a pathway of relatively low electrical resistance. The electrosurgical energy will follow through the plasma to cut, coagulate, desiccate, or fulgurate blood or tissue of the patient. There is no physical contact required between an electrode and the tissue treated.
Electrosurgical systems that do not incorporate a source of regulated gas can ionize the ambient air between the active electrode and the patient. The plasma that is thereby created will conduct the electrosurgical energy to the patient, although the plasma arc will typically appear more spatially dispersed compared with systems that have a regulated flow of ionizable gas.
One of the difficulties in using a plasma is its initiation. A strong electrical field is required to accelerate enough free electrons within the gas such that a cascade of ionizing collisions is initiated which creates the plasma. This is sometimes called “igniting” the plasma. Once a plasma is ignited, it may be sustained at lower electrical field potentials.
Several techniques are presently used to create strong electrical fields that can ignite the plasma. One technique is to move the tip of an electrode very close to the surgical site. The electric field along a path between an electrode and the surgical site increases as their separation decreases, and may reach a level sufficient to ignite the plasma. The drawback of this method is that a surgeon must carefully manipulate the electrode to move it close to the surgical site without actually touching the tissue. If the electrode comes in contact with the tissue it may stick, causing eschar to deposit on the electrode. During laparoscopic procedures, it is often difficult for a surgeon to sense the proximity of the electrode to the tissue.
Another technique to ignite plasma is to use a pointed electrode which will generate a stronger electrical field at the tip of the electrode. However, a pointed electrode may be undesirable if the surgeon requires a blade-shaped electrode for cutting and other tissue manipulation. Yet another technique is to provide high voltage spikes to the surgical electrode until a detector has indicated a closed circuit with the return electrode. Once a closed circuit is detected, the high voltage spikes are terminated and the electrosurgical generator returns to its normal waveform output. While this technique is effective, it requires complicated electronics and components capable of withstanding the high voltages.
U.S. Pat. No. 4,060,088 relates to a monopolar electrosurgical method and apparatus for coagulation by fulguration. The apparatus has source of inert ionized gas which surrounds a tubular electrosurgical electrode. There is also disclosed a source of periodic bursts of electrosurgical energy used to initiate the plasma arc. Only one electrode is disclosed on the electrosurgical apparatus so that the device is monopolar.
U.S. Pat. No. 4,781,175 teaches the application of an ionizable gas jet to the tissue to clear bodily fluids and coagulate or achieve fulguration in the form of an improved eschar using an instrument having a conduit for the flow of gas at a predetermined flow rate about a centrally located electrode for electrosurgical energy. Circuitry and computer logic are shown to control the gas jet flow and the electrosurgical energy. No return path for the electrosurgical energy is provided.
U.S. Pat. Nos. 3,970,088, 3,987,795 and 4,043,342 describe sesquipolar electrodes on an instrument used to apply electrosurgical energy to an operative site.
U.S. Pat. No. 4,041,952 employs a switch on a forceps used as monopolar or bipolar during treatment of the patient with electrosurgery.
U.S. Pat. No. 4,890,610 discloses a pair of bipolar forceps comprising coined metallic conductive blades that are each over-molded with a plastic insulator to leave exposed tips at the patient end and connector terminals for electrosurgical energy at the opposite ends.
U.S. Pat. No. 4,492,231 teaches a bipolar circuit to provide non-stick coagulation by use of a good thermal conductor and minimal contact relative to the volume of conductive material in the tines of the forceps.
U.S. Pat. No. 4,060,088 relates to a monopolar electrosurgical unit in combination with an ionizable gas delivery system.
U.S. Pat. No. 4,040,426 shows a method and apparatus for initiating an electrical discharge in the ionizable gas.
U.S. Pat. No. 4,901,719 teaches a monopolar electrosurgical unit in combination with an ionizable gas delivery system including a gas conducting means.
U.S. Pat. No. 4,429,694 shows a solid-state electrosurgical generator which provides output waveforms that are optimized for electrosurgical fulguration. The fulguration output circuitry consists of a radio-frequency tank circuit which is periodically pulsed to produce a periodic damped-sinusoidal output waveform. However, the damping factor is sufficiently low so that many cycles of the waveform occur between periodic input pulses. Although the duty cycle is relatively high compared to prior art devices, cutting and burning effects are prevented by a high impedance output which internally limits fulguration arc current. The fulgurating arc developed by the device is longer and more consistent than that developed by previous devices thereby resulting in superior fulguration.
U.S. Pat. No. 4,901,720 discloses an electrosurgical generator in an electrosurgical unit (ESU) controls the repetition rate and the energy content of bursts of RF energy delivered to a gas jet supplied by the ESU, in order to maintain RF leakage current within acceptable limits while still achieving a sufficient state of ionization in the gas jet to reliably initiate the conduction of arcs to the tissue. The repetition rate of the RF bursts is substantially reduced in an inactive state when no arcs are delivered. A relatively small number of the RF bursts delivered during the inactive state have an increased or boosted energy content to assure an adequate ionization state in the gas jet.
U.S. Pat. No. 5,088,997 shows a device for enhancing the safety and efficiency of a hand-operated electrosurgical pencil having an electrode with a distal end defining a tip for cutting or coagulating biological tissue, which device comprises a nose piece adapted to be mounted about said electrode and containing conduit means defining converging pathways for streams of gas which impinge obliquely on said electrode at or near the tip thereof, and electrosurgical apparatus incorporating said device and a method for coagulating or cutting biological tissue using said apparatus.
U.S. Pat. No. 6,213,999 describes an apparatus and method for igniting plasma in a surgical system is disclosed. A corona discharge is generated on a surgical handpiece which is used to ignite a plasma arc for surgical operations. The advantages include greater reliability and repeatability of plasma arc ignition. The apparatus comprises a handpiece incorporating an active electrode, a passage for ionizable gas, and a corona return electrode. The corona return electrode has a terminus on the holder and near the distal end of the holder. The corona return electrode is electrically connected to the return path of the electrosurgical generator. A non-uniform electric field is generated between the active electrode and the corona return electrode of sufficient strength so that a corona is formed near the active electrode. A separate return electrode may be on the patient, or the apparatus may be configured for bipolar electrosurgical operation by carrying the return electrode on the handpiece. A dielectric material separates the active electrode and the corona return electrode. There is substantially capacitive coupling between the active electrode and the corona return electrode. There is substantially resistive coupling between the active electrode and the return electrode.
Additional examples of the prior art are found in U.S. Pat. Nos. 1,889,609; 2,835,254; 3,577,030; 3,949,266; 4,559,943; 4,818,916; 4,887,005; 5,302,881; 5,325,019; 5,669,904; 5,710,486; 5,717,293; 5,801,489; 5,815,047; 5,917,286; 6,046,546; 6,181,068; 6,222,321; and 6,262,538.